1. Field of the Invention
The present invention relates to a piston of an engine, particularly a piston of an engine that reduces damage, noise, vibration due to abnormal combustion by reducing the temperature of a combustion chamber through smooth cooling.
2. Description of Related Art
As shown in FIG. 1, a combustion chamber 4 of an engine is formed by the upper surface of a piston 2 disposed in a cylinder block 1 and a cylinder head 3 disposed on a gasket on the upper surface of the cylinder block 1 (a recessed upper surface of the combustion that covers the upper portion of a cylinder bore is formed on the lower surface of the cylinder head 3).
Piston 2 is connected to a crankshaft through a connecting rod 5 to be able to convert up-down motion of piston 2 into rotary motion.
FIG. 2A is a plan view of piston 2, FIG. 2B is a front view, FIG. 2C is a cross-sectional view taken along the line A-A in FIG. 2A, FIG. 2D is a bottom view of piston 2 (seen in direction A in FIG. 2A), and FIG. 2E is a plan view of the bottom of the crown of the piston.
As shown in the figures, valve pockets (2c: pocket for an exhaust valve, 2d: pocket for an intake valve) that prevent collision of valves and the piston at the maximum cycle of the intake/exhaust valves are formed on the upper surface of piston 2, that is, the upper surface of crown 2a. The lower surface of crown 2a in the piston is recessed upward (except for pin bosses 2b) and pin bosses 2b are formed to face each other and has pin holes 2b′ formed through the pin bosses 2b, such that a small end of the connecting rod is connected with a piston hole 2b′ by a piston pin.
On the other hand, in an engine equipped with a turbocharger, when the compression ratio in combustion chamber 4 is excessively increased by excessive supply, abnormal combustion, such as knocking, is caused by rapid mix with excessive air around the top dead center in combustion.
Therefore, the main parts of the engine are damaged by high temperature and pressure due to the abnormal combustion, such as damage to the intake/exhaust valves, breakage and sticking of the piston, and crack in the valve bridge of the cylinder head, which decreases durability of the engine.
Further, there was a problem in that combustion noise is caused by the abnormal combustion when a vehicle starts or changes the speed.
Further, there was a problem in that abnormal vibration is caused in the engine by the abnormal combustion.
In the above cases, combustion process due to abnormal ignition is prevented by delaying spark (ignition) timing or decreasing the temperature in combustion chamber 4. However, when the spark timing is delayed, engine power is reduced, and when a water jacket (cooling water passage) is provided to the cylinder head around the combustion chamber to decrease the temperature in the combustion chamber, the material of the cylinder head should be changed.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.